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New techniques may allow purebred bison calves bearing the genes of the animals that originally populated North America to be reproduced disease-free. Most of today's bison descended from animals cross-bred with domestic cattle.

"What does a two-month-old bison calf in the Bronx have to do with the future of its species? Quite a lot, it turns out.

After being slaughtered to near extinction in the 19th century, the American plains bison (Bison bison bison) has become a bit of a conservation success story, albeit with a few important caveats. Today as many as half a million bison live in the United States, but most of them are genetically impure due to a misguided attempt to crossbreed bison with domestic cattle in the early 20th century. The crossbred bison, which live exclusively in commercial herds, contain what are referred to as "ancestral cattle genes" representing up to 2 percent of their DNA—a not-so-insignificant amount that makes them essentially useless for conservation purposes. Meanwhile, about 40 percent of the 20,000 or so remaining pure bison living in Yellowstone National Park and a few other government-owned herds have, over the years, been exposed to diseases such as brucellosis, which can cause cattle to abort their pregnancies. Many ranchers and other people fear these diseases could leap into domestic cattle or other species. This concern has to date prevented efforts to expand purebred bison populations into new herds.

The bison calf in the Bronx, which is not only genetically pure but also free of disease, could be the first step in changing that. "